1. Anaerobic Threshold • Exceed the CV system’s ability to provide oxygen during exercise and the extra energy must be produced by the anaerobic/lactic acid system. This produces lactic acid and can be maintained only for a few minutes. See the next slide and chart:

2. The athlete below was running with a heart monitor. As the speed and work load increased so did the heart rate. The increase is linear until 190 bpm.At this point it flattens out. 190 is the anaerobic threshold and Max VO2 for the athlete. As speed and work increase the CV system cannot supply enough O2 and energy begins to be created Anaerobically (without O2). Lactic Acid begins to accumulate and the runner will fatigue quickly, unless the work rate drops down below 190 bpm and into the aerobic zone again. This is called Anaerobic Threshold.

3. Glucose store • Another limiting factor to how long you can produce energy is the amount of glucose stored at the muscle. Most people store up to 1 to 2 hours of glucose for use. When it runs out it must be replenished in order to continue exercise. This process occurs over about a 24 hour span and requires rest and proper diet to replace the fuel. Complex carbs are the best choices for restoring glucose. This is one of the primary reasons for limiting training and competitions to less than 2 hours.